Spectral sensitization is a very important stage in the production of silver halide photographic materials which have high-sensitivity and excellent stability. Many spectral sensitizing agents have been developed, and techniques for the use thereof such as supersensitization methods and addition methods, have been developed.
Spectral sensitizing agents such as cyanine dyes, merocyanine dyes, rhodancyanine dyes, etc., are known as spectral sensitizing dyes for use in spectral sensitization. These agents are used either alone or in combination (e.g., for the purpose of supersensitization).
There are many requirements for the sensitizing dyes used in photographic materials to meet. For example, sensitizing dyes must meet the requirements that high spectral sensitivity can be obtained, that fogging is not increased, that changes in the sensitivity, gradation and fog of samples excellent in characteristics during exposure (e.g., latent image stability, reciprocity characteristics, temperature and humidity dependence during exposure, etc.) are small during storage before exposure, and that the dyes are not left behind in the photographic materials after development.
Among these requirements, high sensitivity and high stability during storage are essential. Many attempts have been made.
For example, various compounds have been proposed in JP-A-60-202436 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-220339, JP-A-60-225147, JP-A-61-123834, JP-A-62-87953, JP-A-63-264743, JP-A-1-155334, JP-A-1-177533, JP-A-1-198743, JP-A-1-216342, JP-A-2-42, JP-B-60-57583 (the term "JP-B" as used herein means an "examined Japanese patent publication") and U.S. Pat. 4,618,570. However, the level of improvement is still not sufficient.
Further it is important that various dyes are added to silver halide photographic materials to improve their sharpness and color separation power.
Conventional pentamethinecyanine dyes wherein the 2- and 4-positions on the methine chain are substituted by a trimethylene crosslinking group and further the 1- and 5-positions are combined together with the N-position of the basic nucleus to form a ring include 2,2'-dimethyltrimethylene-crosslinked dyes (the following A, B and C) described in J. Am. Chem. Soc., Vol. 109, pp. 5808-5813 (1987), J. Org. Chem., Vol. 55, pp. 49-57 (1990) and Prc. Electrochem. Soc., Vol. 88, No. 14, pp. 97-104 (1988), and unsubstituted trimethylene-crosslinked dye (the following D) described in Ukr. Khim. Zh., Vol. 14, No. 11, pp. 1165-1170 (1975). The use of the dye A in microcrystalline silver bromide is reported in Prc. Electrochem. Soc., Vol. 88, No. 14, pp. 97-104 (1988).
However, dyes having a trimethylene crosslinked group wherein the 2-position of the above-described trimethylene-crosslinked group is only once substituted by an alkyl group, an aryl group or a heterocyclic group according to the present invention, are not known, nor of course is the photographic performance thereof in silver halide photographic materials. ##STR2##
Supersensitization is described in Photographic Science and Engineering, vol. 13, pp. 13-17 (1969), ibid., Vol. 18, pp. 418-430 (1974), and James, The Theory of the Photographic Process, the fourth edition, p. 259 (Macmillan 1977). It is known that high sensitivity can be obtained by properly choosing the sensitizing dyes and supersensitizing agents.